I. Cmp.

Path.

Malignant

199” Vol.

106, 315-318

Schwannoma

Arising from in a Rat

the Trigeminal

Nerve

M. Yoshida To.xicologv Research Center, Imamichi Institute for Animal Reproduction, Dejima-mura. Niihariygun. Ibaraki 300-01, japan

1103 Fukqn.

Introduction Trigeminal schwannomas can be induced by methyl and ethyl nitrosourea in rats, but naturally occurring intracranial schwannomas in rats are infrequent (Wechsler, Pfeiffer, Swenberg and Koestner, 1973). In man, malignant schwannomas arising from the intracranial trigeminal nerve are also rare (Horie, Akagi, Taguchi, Yoshino, Hayashi, Takahashi and Akagi, 1990). This report describes the macroscopic, histological, ultrastructural and immunohistochemical features of a spontaneous malignant trigeminal schwannoma in a rat. Case Report A 28-week-old male Sic : Wistar rat (SPF animal, Sizuoka Laboratory i\nimal Corporation, Hamamatsu, Japan) was killed after rapid loss of body weight and scvc’re loss of mobility. At necropsy, a white soft mass 1 cm in diameter was found at the bottom of the cranial cavity (Fig. 1 j. The pituitary gland and the intracranial segments of the trigeminal nerve were involved in this mass. Although the ventral surface of the brain was deformed by the mass, the latter was well separated from thr brain. Other body organs showed no macroscopic abnormalities. Materials

and

Methods

The growth and other organs were fixed in 10 per cent neutral buffered formalill, embedded in paraffin wax, sectioned, stained with haematoxylin and eosin (HE;, Azan-Mallory stain and by the periodic acid-Schiff (PAS) reaction. Sections embedded in paraffin wax were stained with rabbit anti-human sera and iIt1 avidin-biotin-peroxidase complex [ABC) kit (Vector Laboratories, Burlingame, C,\, U.S.iz.) for immunohistochemistry. Antisera to S-100 protein (Dako Corporation, Glostrup, Denmark) ~ glial fibrillary acid protein j GFAP) (Dako Corporation; and vimentin (*Medic, Hamburg, Germany) were used at dilutions of 1 in 500, 1 in 500 and I in 50, respectively, with the ABC kit. The procedures described by Hsu, Kaine and Fanger ( 1985) were used for the remaining steps. As controls, an appropriatr dilution of normal rabbit serum was substituted for the primar) antibody. These control sections displayed no positive staining. Cubes ( 1 mm”) of‘ the mass were fixed in 3 pt.1 cent glutaraldehyde with 0.1 M phosphate buffer, post-fixed in 1 per writ osmium tetroxide, dehydrated in alcohol and buthy glycidil ethrr and embedded in E;poll.

316 Ultrathin sections were stained with an electron microscope.

M.

Yoshida

uranyl

acetate and lead citrate and examinrci

Mitt)

Results

Histologically, the tumour was composed of densely packed, uniform cells (Fig. 2). No tendency to nuclear palisading was observed in any part of the tumour. The tumour consisted of spindle-shaped cells with pale eosinophilic cytoplasm, indistinct cell borders and oval or round nuclei. Mitotic figures were frequent, but pleomorphism was not marked (Fig. 2). The stroma of the tumour was scant and some collagen was observed. At the periphery of the tumour, the tumour cells proliferated along trigeminal nerve sheaths (Fig. 3;. Decalcified sections of the intracranial region revealed invasion of both trigeminal ganglia with tumour cells. The latter did not react with PAS or with antibodies to S-100 protein, GFAP or vimentin. No metastases were recognized. Ultrastructurally, most of the tumour consisted of parallel arrangements of spindle-shaped cells with abundant and well developed long cell processes (Fig. 4). Some cell processes showed infolding structures (Fig. 4 insert). Fragmented external lamellae were often observed on tumour cells and their processes (Fig. 5). A few intercellular junctions were found in neighbouring tumour cells. In some areas, the tumour showed a loosely packed pattern, like the Antoni type B pattern in human schwannomas. The cytoplasm of the neoplastic cells contained predominantly free ribosomes, some rough endoplasmic reticulum, mitochondria, lysosomes and a few intermediate filaments. Sparse collagen fibres were scattered among the tumour cells in the stroma. Discussion

The malignant schwannoma in man is well known for being difficult to diagnose by light microscopy alone, because of its hypercellularity and pleomorphism (Henderson, Papakimitriou and Coleman, 1986; Dickersin, 1987). Positive staining for S-100 protein was reported to be a useful marker for schwannoma in man and rats (Erlandson and Woodruff, 1982; Gough, Hanna, Barsoum, Moore and Sturgess, 1986; Laber-Laird, Jokinen and Jerome, 1988; Rice and Ward, 1988; Horie el al., 1990). However, some investigators have found that many malignant schwannomas were negative for S-100 protein staining and that diagnosis of malignant schwannoma should be supported by ultrastructural characteristics of schwannoma, such as external lamellae, cell processes and infolding cell processes or pseudomexaxons (Erlandson and Woodruff, 1982; Gough et al., 1986; Henderson et al., 1986; Dickersin, 1987; Laber-Laird et al., 1988; Rice and Ward, 1988; Horie et al., 1990). The

tumour described possessedthe features of malignant schwannoma. Its malignancy, indicated by frequency of mitosis and abundant free ribosomes, may have been the cause of its negative reaction to the S-100 protein antibody. The reason for the negati1.e reaction to vimentin antibody is not known, but

Malignant

Schwannoma

Fig

I

Gross appearance of malignant schwannoma. bottom of the intracranial cavity.

Fig

2

Microscopic features of the tumour. were observed. HE x 156.

Fig

3.

Periphery of th e tumour. sheaths. HE x 156.

Note

Fig 4.

Elertron micrograph. Spindle-shaped in parallel. Fine collagen is scattered thin cell process. Bar = 1 pm.

I&

Ektron

5.

micrograph.

Segmented

The turnour

Hyperl~cllularitv invasive turnour within

external

3 17

in a Rat

was found

as a white,

and an incrrased

proliferation

of tllmour

soft mass at t hr

number

of mitotic

cells along

trigeminal

tiyu~t~ m’I-\ c

cells with abundant long crll processes werr arran~rtl the stroma. Bar= 4 pm. Insert: Infolding structure 01 lamella

iarrowheads\

was observed.

Bar=

1 pm

318

M.

Yoshida

the numbers of intermediate filaments observed may have been too few to react to immunohistochemical staining. In man and rats, malignant schwannomas arising in the trigeminal nerve were reported to proliferate around the remaining non-neoplastic nerve sheaths or ganglion cells (Wechsler et al., 1973, Horie et al., 1990). In the present case, the invasion along the trigeminal nerve sheaths suggested that this tumour was a malignant schwannoma arising from the trigeminal nerve. This report emphasizes the value of ultrastructural examination in the diagnosis of malignant schwannomas, not only in man but also in rats. Acknowledgment The author thanks helpful advice.

Dr K. Mitsumori,

National

Institute

of Hygienic

Science,

for

References Dickersin, G. R. (1987). The electron microscopic spectrum of nerve sheath tumors. LJltrastructural Pathology, 11, 1Q3- 146. Erlandson, R. A. and Woodruff, J. IM. (1982). Peripheral nerve sheath tumors. An electron microscopic study of 43 cases. Cancer, 49, 273-287. Gough, A. W., Hanna, W., Barsoum, N. J., Moore, J. and Sturgess, J. M. (1986). Morphologic and immunohistochemical features of two spontaneous peripheral nerve tumors in Wistar rats. Veterinary Pathology, 23, 68-73. Henderson, D. W., Papakimitriou, J. M. and Coleman, M. (1986). Peripheral neural tumors. In LJltrastructural .4ppearancr of Tumors, 2nd Edit. Churchill Livingstone, Edinburgh, pp. 206-2 16. Horie, Y., Akagi, S., Taguchi, K., Yoshino, T., Hayashi, K., Takahashi, K. and Akagi, T. (1990). Malignant schwannoma arising in the intracranial trigeminal nerve. Acta Pathologira Japonica, 40, 2 I9-225. Hsu, S., Raine, L. and Fanger, H. (1985). Use of avidin-biotin-peroxidase complex (ABC) in immunoperoxidase techniques: a comparison between ABC and unlabeled antibody (PAP) procedures. Journal of Histochemistry and CytochemistTy, 29, 577-580. Laber-Laird, K. E., Jokinen, M. P. and Jerome, C. P. (1988). Naturally occurring schwannoma in a Fischer 344 rat. Veterinary Pathology, 25, 320-322. Rice, J. M. and Ward, J. M. (1988). S ch wannoma (induced), cranial, spinal and peripheral nerve, rat. In Monographs on Pathology of Laborator?, Animals, Nervous @stern. T. C. Jone, U. Mohr and R. D. Hunt, Eds, Springer-Verlag, Berlin, pp. 154-160. Wechsler, W., Pfeiffer, S. E., Swenberg, J. A. and Koestner, A. (1973). S-100 protein in methyl- and ethylnitrosourea induced tumors of the rat nervous system. Act& .,~e~&ropathol(lgucl f Berlin), 24, 287-303.

c

1

Accepted, Received,December August 2501, 29th, 199 1991 1